This invention relates to lasers (including non-oscillating amplifiers).
In the past, lasing has been produced in gases by application of an electric field at a potential sufficient to produce an avalanche breakdown discharge, thereby generating a plasma by ionization and heating (i.e., raising the mean electron energy) the plasma sufficiently to pump the gas to its lasing level. It has been asserted that discharge uniformity can be improved, and arcing delayed, by use of an auxiliary discharge to create ionization prior to passage of the main current pulse. Preionization with an electron beam is disclosed, e.g. in Garnsworthy et al., Atmospheric-Pressure Pulsed CO.sub.2 Laser Utilizing Preionization by High-Energy Electrons, Applied Physics Letters, Vol. 19, No. 12, p. 506 (Dec. 15, 1971). Photopreionization (as well as photoionization to help sustain the main discharge) is disclosed, e.g., in Seguin et al., Photoinitiated and Photosustained Laser, Applied Physics Letters, Vol. 21, No. 9, p. 414 (Nov. 1, 1972).
Also, recently, a high energy electron beam has been used as an external ionization source to produce a plasma which is then heated by application of a sustaining electric field at below the avalanche breakdown potential. Such a system is described, e.g., in Fenstermacher et al., Electron-Beam-Controlled Electrical Discharge as a Method of Pumping Large Volumes of CO.sub.2 Laser Media at High Pressure, Applied Physics Letters, Vol. 20, No. 2 (Jan. 15, 1972), pages 56-60, where it is suggested (p. 57) that the plasma might also be produced by an external source of photoionization. Eletskii and Smirnov, A Pulsed Carbon Dioxide Laser, Soviet Physics, Vol. 15, No. 2, p. 109 (August, 1970) discloses an attempt to photoionize cesium as a seed gas in a CO.sub.2 -- N.sub.2 -- He laser employing a below-breakdown sustaining electric field.
R. L. Schriever, Uniform Direct-Current Discharges in Atmospheric Pressure He/N.sub.2 /CO.sub.2 Mixtures Using Gas Additives, Applied Physics Letters, Vol. 20, No. 9, p. 354 (May, 1972) discloses use of benzene, toluene, xylene, and trimethyl benzene as gas additives in a direct-current discharge He -- N.sub.2 -- CO.sub.2 system, and refers to the Eletskii and Smirnov suggestion of cesium as impractical. Seguin, Tulip, and McKen, Enhancement of Photoelectron Density in TEA Lasers Using Additives, Applied Physics Letters, Vol. 23, No. 9, p. 529 (Nov. 1, 1973) discusses the use of triethylamine mixed with tripropylamine as a seed gas additive to a spark initiated CO.sub.2 laser. A Semiannual Technical Report dated December, 1973, by Hughes Research Laboratories, entitled Investigation of UV Photoionization Sustained Discharge for Gas Lasers (covering the reporting period Jan. 2, 1973 - June 30, 1973 under Contract N00014-73-C-0287 sponsored by Advanced Research Projects Agency) discloses the use of tripropylamine as a seed gas in a laser employing a below-breakdown sustaining electric field.
Seguin, Tulip, and McKen, Ultraviolet Photoionization in TEA Lasers,IEEE Journal of Quantum Electronics, Vol.QE-10, No.3,p. 311 (March, 1974) summarizes much of the previous literature and work.
Applicants' publications Observation of Laser Oscillation in a 1 Atmosphere CO.sub.2 -- N.sub.2 -- He Laser Pumped by an Electrically Heated Plasma Generated Via Photoionization, Applied Physics Letters, Vol. 22, No. 2 (January, 1973), and The Feasibility of Producing Laser Plasmas Via Photoionization, IEEE Journal of Quantum Mechanics, Vol. QE-8, pp. 827-832 (November, 1972), taken together, deal with two-step photoionization, with and without seed gases, in CO.sub.2 -- N.sub.2 -- He lasers employing a below-breakdown sustaining electric field, to which invention is directed applicants' U.S. Pat. No. 3,826,997. Tripropylamine, tripentylamine, and tributylamine are disclosed as seed gases.